bought this lower the other day for a first build, and the damn buffer pin wont stay in at all. it looks like they do a cut out so they can put their buffer tube in deeper and failed to thread it all the way. I dont have the castlenut wrench so now I'll have to go buy one. is this typical of DPMS?

Looks like some Bubba smithing. If you screw the extension in too far, you may not be able to close the upper receiver. It appears they wanted to screw it in deep, but it was binding against the retaining pin. So they Bubba-smithed the extension to relieve where it binded.

Originally Posted By bad_company5150:bought this lower the other day for a first build, and the damn buffer pin wont stay in at all. it looks like they do a cut out so they can put their buffer tube in deeper and failed to thread it all the way. I dont have the castlenut wrench so now I'll have to go buy one. is this typical of DPMS?

Was this a complete lower or a kit put on a stripped lower? The cut out is there in the tube for that the pin part of the buffer retainer came come up and as a partial indexer for the stock being squared to the receiver.

You make reference to not threading all the way? Are you talking about the tube of the recevier? There should be plenty of thread on the tube left. The receiver has a ton of thread in front of where you are. So what it look like you need to do is loosen the castle nut, then turn the stock and tube in one more turn. As long as you can turn it a full turn and not make the detent stick. If you can, then at the back of the receiver see if you have tube sticking through that block the upper from coming down. If you do lightly file it back or pull the tube off, File/sand back, reinstall the tube.

It really appears like it was put on one turn too lite and the detent pushed off the little bit of metal that was holding it down.

Who ever ground on that receiver extension knew absolutely nothing about how the buffer retainer functions. Your best bet is to see if the dealer you purchased the lower from will swap out the defective receiver extension. If not, purchase a new one your self.

Originally Posted By BRADLEYBUILT:What if you put it to a belt sander and shave the entire end off square till that cutout is gone? Saves you a few dollers on parts and shipping.

If the receiver extension is for a standard A1/A2 stock, sanding it down flush won’t work. The receiver extension for the A1/A2 stock has a shoulder on it that bottoms out on the rear of the receiver. This shoulder limits how far in the receiver extension can be threaded.

If the receiver extension is for a collapsible stock, sanding it down might work. But the whole end of the receiver extension would have to be redone. Both the bottom of the extension that retains the buffer retainer, and the top of the extension as well.

You can either fit the tube you have to your receiver, or replace your tube. Fitting may require some filing and sanding. Turn the buffer tube in 1 full turn until the buffer pin is secured. File and sand the tube so the upper closes. This shouldn't happen in a new gun.

Note on this photo... there is a half thread on the bottom of the tube that is ground away on the upper portion of the tube. Can you see it on each side?

This is correct.

Many times a carbine tube is cut straight across the tube. Then, when it is threaded into the receiver to properly hold down the detent, as you can see in this photo, with the tube almost, but not quite touching the "tit" on the detent, then the threads protrude at the top. That prevents the upper from closing.

So some dufus unscrews the tube one full turn. Now it is back enough to allow the upper to close, but does not sufficiently hold the detent.

The correct thing to do is simply grind back that upper thread, easily done on a bench grinder and then dress off the rough spots with a wire brush.

Better quality carbine tubes come with that upper thread already trimmed back. And from the appearance in this photo, this was one that was properly shaped to begin with.

Get a new tube and fit it as I have just described.

In the next photo, this tube is not properly installed. It does not thread in enough to properly capture the detent. The person that installed this tube was afraid it would protrude too much at the top and bind with the upper receiver. He was correct. As it is, it may work for a short while, but soon a little wear on the edge of the tube will allow the detent to get loose. FAIL!

This next tube is not properly installed, either. It is threaded in enough to capture the detent, but the top thread of the tube protrudes past the upper receiver where it will bind and wear on the upper receiver. FAIL!

These two improperly installed tubes are not the fault of the DPMS receivers. They would be that way in any receiver.

Are those photos of Ace stocks? The Ace tube is cut with a longer lip on bottom.

What they are is the result of poor installation.

"To my mind it is wholly irresponsible to go into the world incapable of preventing violence, injury, crime, and death. How feeble is the mindset to accept defenselessness. How unnatural. How cheap. How cowardly. How pathetic." --Ted Nugent

this was a DPMS complete lower receiver. any failure is their fault alone. it does have the filing done already and I think it will work fine with one more turn, it just pisses me off they let it through like this.

In the next photo, this tube is not properly installed. It does not thread in enough to properly capture the detent. The person that installed this tube was afraid it would protrude too much at the top and bind with the upper receiver. He was correct. As it is, it may work for a short while, but soon a little wear on the edge of the tube will allow the detent to get loose. FAIL!

This next tube is not properly installed, either. It is threaded in enough to capture the detent, but the top thread of the tube protrudes past the upper receiver where it will bind and wear on the upper receiver. FAIL!

Actually I grabbed the wrong photo and both are of the same lower vs. two different lowers. MOST of the ACE tubes are done with the longer lip. That one is a fixed length rifle buffered skeleton stock so it is not cut that way vs. say the SOCOM.

So as you noted in the second photo it does capature the detent and as you didn't in the first it actually doesn't protrude into the upper. It runs just a hair short of flush. But it is more or less like an A1/A2 tube.

Then again I admit it's hard to tell from a picture and angles certainly change how things look.

I have a buffer tube that has a similar notch to the one you originally pictured, except that the notch is straight and not flaired. It looks to me like you might be able to put one more turn on the tube and the remaining portion of the notch will center on the pin of the buffer retainer as it should.

Just make sure that once you make another turn that there is no metal from the buffer tube extending past the top of the receiver threads that would prevent you installing the upper.

which direction do I turn the castle nut when looking down at a shooters point of view of the weapon? it seems like it would be counter clockwise, but it wont budge. I just bent my CAR wrench trying to get it off.

I just installed a DPMS stock for my son last night, wish my dad had built me an AR when I was 14, it has the same notch. I gave it one more turn and tightened the locking ring, works like a charm. Like another member said, "Give it another turn".

You know I got the same problem with my DPMS lower. I took the A2 stock off and put a Bushy M4 stock on. If I tighten some more my upper would not go into lower, So I just had to live with this (pics below) haven't shot it yet so don't know if it will work. It does keep the pin down though. Any ideas on what I should do? Its a fixed stock so i dont think i can change out the tube.